Wireless communication networks are well known and constantly evolving. For example, UMTS is one of third-generation (3G) cell phone technologies. Currently, the most common form of UMTS uses wideband code division multiple access (W-CDMA) as the underlying air interface, as standardized by the 3GPP (3G partnership project).
Currently, UMTS networks worldwide are being upgraded to increase data rate and capacity for downlink packet data. In order to ensure a further competitiveness of UMTS, various concepts for UMTS long term evolution (LTE) have been investigated to achieve a high-data-rate, low-latency and packet optimized radio access technology.
3GPP LTE (long term evolution) is the name given to a project within the third generation partnership project to improve the UMTS mobile phone standard to cope with future requirements. Goals of the project include improving efficiency, lowering costs, improving services, making use of new spectrum opportunities, and better integration with other open standards. The LTE project is not a standard, but it is expected to result in the new evolved release 8 of the UMTS standard, including mostly or wholly extensions and modifications of the UMTS system.
A characteristic of evolved UMTS is that it is fundamentally based upon transmission control protocol/internet protocol (TCP/IP), the core protocol of the Internet, with built-on higher level services such as voice, video, and messaging.
In modern wireless networks, a sounding reference signal (SRS) is typically transmitted with a wide bandwidth for a base station, or node B, to find a best resource unit (RU), also known as a resource block (RB) or physical resource block (PRB) in the LTE standard for a transmitting from a user equipment (UE), such as a mobile device. However, due to the restrictions on the maximum UE transmission power, the channel quality indication (CQI) measurement accuracy is degraded when the received power of the SRS signal is degraded, such as when a UE located near edge of the cell transmits the SRS. This degradation of the SRS may cause errors to arise in the optimum RU assignment and in the modulation and coding scheme (MCS) selection. Therefore, improvements in the transmission of the SRS from the UE help to achieve the maximum user throughput. Accordingly, the SRS is designed to enable channel aware scheduling and fast link adaptation for PUSCH for UL data transmissions. The SRS is also used as a reference (RS) for closed loop power control (PC) for both physical uplink shared channel (PUSCH) and a physical uplink control channel (PUCCH).
Furthermore, SRS can be used to improve/enable the channel aware download (DL) scheduling in time division duplex (TDD) mode. TDD is the application of time-division multiplexing to separate outward and return signals. In particular, TDD emulates full duplex communication over a half duplex communication link and provides benefits where the asymmetry of the uplink and downlink data speed is variable.